diff --git a/modules/index.d.ts b/modules/index.d.ts
index 0fedae8..3244fab 100644
--- a/modules/index.d.ts
+++ b/modules/index.d.ts
@@ -33,5 +33,6 @@ export {
   __createBinding,
   __addDisposableResource,
   __disposeResources,
+  __rewriteRelativeImportExtension,
 } from '../tslib.js';
 export * as default from '../tslib.js';
diff --git a/modules/index.js b/modules/index.js
index af9f5ac..c91f618 100644
--- a/modules/index.js
+++ b/modules/index.js
@@ -31,6 +31,7 @@ const {
     __classPrivateFieldIn,
     __addDisposableResource,
     __disposeResources,
+    __rewriteRelativeImportExtension,
 } = tslib;
 export {
     __extends,
@@ -64,5 +65,6 @@ export {
     __classPrivateFieldIn,
     __addDisposableResource,
     __disposeResources,
+    __rewriteRelativeImportExtension,
 };
 export default tslib;
diff --git a/test/node/rewriteRelativeImportExtension.test.js b/test/node/rewriteRelativeImportExtension.test.js
new file mode 100644
index 0000000..6eb83d5
--- /dev/null
+++ b/test/node/rewriteRelativeImportExtension.test.js
@@ -0,0 +1,57 @@
+import assert from "node:assert";
+import { test } from "node:test";
+import { testHelper } from "./testHelper.js";
+
+testHelper("__rewriteRelativeImportExtension", __rewriteRelativeImportExtension => {
+  test("rewrites relative .ts to .js", () => {
+    assert.equal(__rewriteRelativeImportExtension("./foo.ts"), "./foo.js");
+    assert.equal(__rewriteRelativeImportExtension("../foo.ts"), "../foo.js");
+    assert.equal(__rewriteRelativeImportExtension("../../foo.ts"), "../../foo.js");
+    assert.equal(__rewriteRelativeImportExtension("./foo.TS"), "./foo.js");
+    assert.equal(__rewriteRelativeImportExtension("./foo.Ts"), "./foo.js");
+    assert.equal(__rewriteRelativeImportExtension("./foo/.hidden/foo.ts"), "./foo/.hidden/foo.js");
+  });
+
+  test("rewrites other TypeScript extensions", () => {
+    assert.equal(__rewriteRelativeImportExtension("./foo.mts"), "./foo.mjs");
+    assert.equal(__rewriteRelativeImportExtension("./foo.cts"), "./foo.cjs");
+    assert.equal(__rewriteRelativeImportExtension("./foo.tsx"), "./foo.js");
+    assert.equal(__rewriteRelativeImportExtension("./foo.tsx", true), "./foo.jsx");
+    assert.equal(__rewriteRelativeImportExtension("./foo.Tsx", true), "./foo.jsx");
+    assert.equal(__rewriteRelativeImportExtension("./foo.d.css.mts"), "./foo.d.css.mjs");
+    assert.equal(__rewriteRelativeImportExtension("./foo.d.tsx"), "./foo.d.js");
+  });
+
+  test("does not rewrite other extensions", () => {
+    assert.equal(__rewriteRelativeImportExtension("./foo.js"), "./foo.js");
+    assert.equal(__rewriteRelativeImportExtension("./foo.mjs"), "./foo.mjs");
+    assert.equal(__rewriteRelativeImportExtension("./foo.cjs"), "./foo.cjs");
+    assert.equal(__rewriteRelativeImportExtension("./foo.jsx"), "./foo.jsx");
+    assert.equal(__rewriteRelativeImportExtension("./foo.json"), "./foo.json");
+    assert.equal(__rewriteRelativeImportExtension("./foo.css"), "./foo.css");
+    assert.equal(__rewriteRelativeImportExtension("./foo"), "./foo");
+    assert.equal(__rewriteRelativeImportExtension("./foo.d.php?q=1.ts"), "./foo.d.php?q=1.ts");
+  });
+
+  test("does not rewrite non-relative imports", () => {
+    assert.equal(__rewriteRelativeImportExtension("foo.ts"), "foo.ts");
+    assert.equal(__rewriteRelativeImportExtension("foo.mts"), "foo.mts");
+    assert.equal(__rewriteRelativeImportExtension("foo.cts"), "foo.cts");
+    assert.equal(__rewriteRelativeImportExtension("foo.tsx"), "foo.tsx");
+    assert.equal(__rewriteRelativeImportExtension("foo.js"), "foo.js");
+    assert.equal(__rewriteRelativeImportExtension("foo.mjs"), "foo.mjs");
+    assert.equal(__rewriteRelativeImportExtension("foo.cjs"), "foo.cjs");
+    assert.equal(__rewriteRelativeImportExtension("foo.jsx"), "foo.jsx");
+    assert.equal(__rewriteRelativeImportExtension("foo.json"), "foo.json");
+    assert.equal(__rewriteRelativeImportExtension("foo.css"), "foo.css");
+    assert.equal(__rewriteRelativeImportExtension("foo"), "foo");
+  });
+
+  test("does not rewrite declaration file extensions", () => {
+    assert.equal(__rewriteRelativeImportExtension("./foo.d.ts"), "./foo.d.ts");
+    assert.equal(__rewriteRelativeImportExtension("./foo.d.mts"), "./foo.d.mts");
+    assert.equal(__rewriteRelativeImportExtension("./foo.d.cts"), "./foo.d.cts");
+    assert.equal(__rewriteRelativeImportExtension("./foo.d.css.ts"), "./foo.d.css.ts");
+    assert.equal(__rewriteRelativeImportExtension("./foo.D.ts"), "./foo.D.ts");
+  });
+});
diff --git a/tslib.d.ts b/tslib.d.ts
index 4576221..f23df55 100644
--- a/tslib.d.ts
+++ b/tslib.d.ts
@@ -451,3 +451,10 @@ export declare function __addDisposableResource<T>(env: { stack: { value?: unkno
  * @seealso {@link __addDisposableResource}
  */
 export declare function __disposeResources(env: { stack: { value?: unknown, dispose?: Function, async: boolean }[]; error: unknown; hasError: boolean; }): any;
+
+/**
+ * Transforms a relative import specifier ending in a non-declaration TypeScript file extension to its JavaScript file extension counterpart.
+ * @param path The import specifier.
+ * @param preserveJsx Causes '*.tsx' to transform to '*.jsx' instead of '*.js'. Should be true when `--jsx` is set to `preserve`.
+ */
+export declare function __rewriteRelativeImportExtension(path: string, preserveJsx?: boolean): string;
\ No newline at end of file
diff --git a/tslib.es6.js b/tslib.es6.js
index 9365006..ddd87f6 100644
--- a/tslib.es6.js
+++ b/tslib.es6.js
@@ -348,6 +348,15 @@ export function __disposeResources(env) {
     return next();
 }
 
+export function __rewriteRelativeImportExtension(path, preserveJsx) {
+    if (typeof path === "string" && /^\.\.?\//.test(path)) {
+        return path.replace(/\.(tsx)$|((?:\.d)?)((?:\.[^./]+?)?)\.([cm]?)ts$/i, function (m, tsx, d, ext, cm) {
+            return tsx ? preserveJsx ? ".jsx" : ".js" : d && (!ext || !cm) ? m : (d + ext + "." + cm.toLowerCase() + "js");
+        });
+    }
+    return path;
+}
+
 export default {
     __extends: __extends,
     __assign: __assign,
@@ -380,4 +389,5 @@ export default {
     __classPrivateFieldIn: __classPrivateFieldIn,
     __addDisposableResource: __addDisposableResource,
     __disposeResources: __disposeResources,
+    __rewriteRelativeImportExtension: __rewriteRelativeImportExtension,
 };
diff --git a/tslib.es6.mjs b/tslib.es6.mjs
index e669963..a1d9ef5 100644
--- a/tslib.es6.mjs
+++ b/tslib.es6.mjs
@@ -347,6 +347,15 @@ export function __disposeResources(env) {
   return next();
 }
 
+export function __rewriteRelativeImportExtension(path, preserveJsx) {
+  if (typeof path === "string" && /^\.\.?\//.test(path)) {
+      return path.replace(/\.(tsx)$|((?:\.d)?)((?:\.[^./]+?)?)\.([cm]?)ts$/i, function (m, tsx, d, ext, cm) {
+          return tsx ? preserveJsx ? ".jsx" : ".js" : d && (!ext || !cm) ? m : (d + ext + "." + cm.toLowerCase() + "js");
+      });
+  }
+  return path;
+}
+
 export default {
   __extends,
   __assign,
@@ -379,4 +388,5 @@ export default {
   __classPrivateFieldIn,
   __addDisposableResource,
   __disposeResources,
+  __rewriteRelativeImportExtension,
 };
diff --git a/tslib.js b/tslib.js
index e53dd2f..95beb91 100644
--- a/tslib.js
+++ b/tslib.js
@@ -44,6 +44,7 @@ var __classPrivateFieldIn;
 var __createBinding;
 var __addDisposableResource;
 var __disposeResources;
+var __rewriteRelativeImportExtension;
 (function (factory) {
     var root = typeof global === "object" ? global : typeof self === "object" ? self : typeof this === "object" ? this : {};
     if (typeof define === "function" && define.amd) {
@@ -395,6 +396,15 @@ var __disposeResources;
         return next();
     };
 
+    __rewriteRelativeImportExtension = function (path, preserveJsx) {
+        if (typeof path === "string" && /^\.\.?\//.test(path)) {
+            return path.replace(/\.(tsx)$|((?:\.d)?)((?:\.[^./]+?)?)\.([cm]?)ts$/i, function (m, tsx, d, ext, cm) {
+                return tsx ? preserveJsx ? ".jsx" : ".js" : d && (!ext || !cm) ? m : (d + ext + "." + cm.toLowerCase() + "js");
+            });
+        }
+        return path;
+    };
+
     exporter("__extends", __extends);
     exporter("__assign", __assign);
     exporter("__rest", __rest);
@@ -426,6 +436,7 @@ var __disposeResources;
     exporter("__classPrivateFieldIn", __classPrivateFieldIn);
     exporter("__addDisposableResource", __addDisposableResource);
     exporter("__disposeResources", __disposeResources);
+    exporter("__rewriteRelativeImportExtension", __rewriteRelativeImportExtension);
 });
 
 0 && (module.exports = {
@@ -460,4 +471,5 @@ var __disposeResources;
     __classPrivateFieldIn,
     __addDisposableResource,
     __disposeResources,
+    __rewriteRelativeImportExtension,
 });